Ultrasound imaging of the coronary vessels of a patient can provide physicians with valuable information regarding the identify the shape of a blood vessel, its density, its composition that can be useful in the diagnosis and/or treatment of a patient. For example, such information may show the extent of a stenosis in a patient, reveal progression of disease, determine the vulnerability of the atherosclerotic plaque for causing myocardial infarction, help determine whether procedures such as angioplasty, stenting or atherectomy are indicated, or whether more invasive procedures are warranted.
Currently, intravascular ultrasound (IVUS) devices use reflected ultrasound data to reproduce or image a blood vessel. In a typical ultrasound imaging system, an ultrasonic transducer is attached to the end of a catheter that is carefully maneuvered through a patient's body to a point of interest such as within a blood vessel. The transducer may be a single-element crystal or probe that is mechanically scanned or rotated back and forth to cover a sector over a selected angular range. Acoustic signals are then transmitted and echoes (or backscatter) from these acoustic signals are received. As the probe is swept through the sector, many acoustic lines are processed building up a sector-shaped image of the patient. These signals may then be processed using well known techniques and transformed into a gray scale image of the vasculature on a computer console in the catheter lab, i.e. an IVUS image.
More recently, the radio frequency signal from the backscatter data has been gathered and correlated with known histology data to permit further analysis and classification of the vasculature. This new Virtual Histology™ technology provides the ability to identify boundary features within the vasculature and plaque and to determine the composition of each patient's atherosclerotic plaques from the RF backscatter data. Currently, Virtual Histology mapping is accomplished by transforming the RF backscatter signal from an IVUS catheter into the frequency domain and then analyzing various power spectral characteristics to classify tissue in windows along each IVUS scan line according to a database, or classification tree, containing the specific spectrum RF signals for four plaque types, fibrous, fibro-fatty, dense calcium and necrotic core. Using this technology, Virtual Histology™ (VH) images generated from IVUS data can now show four plaque component types.
The VH databases, or classification trees, used to correlate the patient's IVUS data and identify tissue type are compiled by examining RF backscatter data from known histologic tissue types and correlating the spectral characteristics of the backscatter data with a specific tissue type. However, the VH classification trees must be computed using IVUS catheters operating at a specific frequency since data obtained using catheters operating at other frequencies may result in different spectral characteristics for a given tissue. Thus, separate VH classification trees must be generated for each catheter operating frequency and the patient data obtained from a catheter operating at a specific frequency must be correlated with the classification tree for that operating frequency in order to achieve an accurate mapping of the patients vasculature and classification of the vascular tissue and plaque type. Currently IVUS catheters operating at 20 MHz, 30 MHz and 40 MHz are commercially available. In addition, there are several types of ultrasonic transducers capable of gathering and transmitting the frequency spectrum of RF signal backscattered from vascular tissue needed to characterize the vascular tissue. For example, phased array IVUS catheters or rotational IVUS catheters, such as those disclosed in such as disclosed in U.S. Pat. No. 5,368,037, issued to Eberle and U.S. Pat. No. 5,000,185, issued to Yock, both fully incorporated herein by reference, may be used to gather RF data. However, once again, different VH classification trees must be generated for data obtained from phased array vs. rotational IVUS catheters.
Early imaging catheters typically relied on manual recognition of a catheter type. For example, catheters were color coded according to type then the operator had to manually input this information into an operation console. Other early alternatives included measuring the catheter resistance to determine the operating frequency or storing catheter information in an EPROM located in the catheter connector. However, with the use of multiple VH classification databases to analyze data from catheters with different operating frequencies or modes of use, the identification and communication of catheter operating information from the catheter to the operation console is critical.
Thus, new devices and methods are needs for identifying information regarding the IVUS catheter being used, for example the catheter type, operational frequency, individual performance characteristics and/or calibration coefficients, etc, and relaying that information to an attached operator's console to assist in selection of the appropriate VH classification tree for analyzing the RF data obtained from the IVUS catheter.